The present invention relates to an apparatus for recording position information of a principal image and to a method of detecting a principal image. More particularly, the invention relates to an apparatus for recording information representing the position of a principal image within a frame at the time of taking an image, and to a method of identifying a principal image in accordance with that position information when a hard copy of the frame is produced.
Known recording media for recording an image include: photographic film used with a photographic camera; a magnetic recording medium used with a video camera and electronic still camera; an IC memory card; and the like. In producing a hard copy, a photographic film generally is used as the recording medium. In one current photographic print system, the photographing conditions and intent of a photographer are estimated from an image recorded on a photographic film, so that a finished photographic print in some cases may become unsatisfactory for the photographer.
Various types of known photographic cameras can record various information on a photographic film at the time of photographing in order to produce a photographic print matching the intent of a photographer. For example, Japanese Patent Laid-open Publication Nos. 51-117632, 52-13333, and 52-30429 describe the recording of illumination light type at the time of photographing on a photographic film. Japanese Patent Laid-open Publication Nos. 63-298233 and 64-21432 describe recording of trimming information. Japanese Patent Laid-open Publications Nos. 50-30517, 55-101932, and 54-2115 describe recording of the type of a principal image, i.e., the image of a principal subject (object).
It is common that photographic prints are regarded as properly finished if a principal image on a color paper has a proper density and color balance regardless of whether a background image is finished improperly to some degree. The above-described conventional methods, however, are associated with a problem in that a finished principal image cannot be properly formed because the position of a principal image cannot be identified. One method of discriminating a principal image is a statistical scheme to estimate that a principal image is present in the center of a frame. However, a principal image is not always present at the center of a frame, thereby posing a problem of a number of erroneous estimations.
Another method is to derive an image of a face from a frame on the empirical assumption that almost all principal images are human faces. For example, Japanese Patent Laid-open Publication No. 52-156624 describes a method wherein the color on a negative image corresponding to flesh color on a positive image (hereinafter, for ease of description, such color will be called simply flesh color) is defined, and the color density at each scanned point within a frame is compared with the defined color to judge whether the pixel is flesh colored. An area having such flesh colored pixels is considered to be a principal image. An average color density within the principal image area is calculated to determine a print exposure amount.
The just-described method is excellent from the standpoint of exposure control, but is not conducive to deriving flesh color pixels from within a frame. Therefore, for example, if a wall having a color similar to flesh color is included within a scene, this wall will be judged erroneously as flesh or skin.
According to a further method disclosed in Japanese Patent Laid-open Publication No. 62-189456, a frame is taken with a TV camera, and the image within the frame is displayed on a monitor to designate a point on a facial image with a light pen or the like. Using the color at the designated point as a reference, pixels having the same or approximately the same color as the reference color are derived automatically, so that the area having such derived pixels is determined to be a facial image area. However, with this method, cumbersome operations are required to designate a point of a facial image with a light pen.